This is from the F1 help:
This account is used for sales transactions only.
This account records the delivery of inventory when the delivery of inventory and the issue of the invoice occur in different posting periods.
There is an option to turn this on or off in the General Settings>BP Tab
From the F1 Help:
When modified, this setting is updated per company, for all users.
Use Shipped Goods Account for Customer
Select this checkbox to enable the postings to the shipped goods account.
When the delivery of inventory and the issue of the invoice occur in different posting periods, you can choose to post the delivery of the inventory to the shipped goods account instead of the COGS account. As such, the delivery of the inventory will be reflected in your Balance Sheet instead of the Profit and Loss statement, and your income and profit will be recorded more accurately.
Once you have selected this checkbox, the Use Shipped Goods Account checkbox on the General sub tab of the Accounting tab of the Business Partner Master Data window will be selected by default for newly added customers.
Essentially it is an accounting function to record the revenue and expense in the same financial period.